[React UI] A couple of fixes

[bsekachev]

Motivation and context

Fixed one issue related with cached data and probably some ambiguity in data streaming
Added error message for case when plugins could not be initialized (infinite loading was before)

How has this been tested?

Manual testing

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2020 Intel Corporation
#
# SPDX-License-Identifier: MIT

Resolve #1944
Related #1965

[coveralls]

Pull Request Test Coverage Report for Build 6686

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 105 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.02%) to 69.062%

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Files with Coverage Reduction	New Missed Lines	%
src/frames.js	3	23.31%
src/session.js	102	54.35%

Totals
Change from base Build 6672:	0.02%
Covered Lines:	11182
Relevant Lines:	15673

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💛 - Coveralls